@article{ValeroBung2018, author = {Valero, Daniel and Bung, Daniel B.}, title = {Vectrino profiler spatial filtering for shear flows based on the mean velocity gradient equation}, series = {Journal of Hydraulic Engineering}, volume = {144}, journal = {Journal of Hydraulic Engineering}, number = {7}, publisher = {ASCE}, address = {Reston, Va.}, issn = {0733-9429}, doi = {10.1061/(ASCE)HY.1943-7900.0001485}, year = {2018}, abstract = {A new methodology is proposed to spatially filter acoustic Doppler velocimetry data from a Vectrino profiler based on the differential mean velocity equation. Lower and upper bounds are formulated in terms of physically based flow constraints. Practical implementation is discussed, and its application is tested against data gathered from an open-channel flow over a stepped macroroughness surface. The method has proven to detect outliers occurring all over the distance range sampled by the Vectrino profiler and has shown to remain applicable out of the region of validity of the velocity gradient equation. Finally, a statistical analysis suggests that physically obtained bounds are asymptotically representative.}, language = {en} } @article{ValeroBungErpicumetal.2022, author = {Valero, Daniel and Bung, Daniel B. and Erpicum, Sebastien and Peltier, Yann and Dewals, Benjamin}, title = {Unsteady shallow meandering flows in rectangular reservoirs: a modal analysis of URANS modelling}, series = {Journal of Hydro-environment Research}, journal = {Journal of Hydro-environment Research}, number = {In Press}, publisher = {Elsevier}, address = {Amsterdam}, issn = {1570-6443}, doi = {10.1016/j.jher.2022.03.002}, year = {2022}, abstract = {Shallow flows are common in natural and human-made environments. Even for simple rectangular shallow reservoirs, recent laboratory experiments show that the developing flow fields are particularly complex, involving large-scale turbulent structures. For specific combinations of reservoir size and hydraulic conditions, a meandering jet can be observed. While some aspects of this pseudo-2D flow pattern can be reproduced using a 2D numerical model, new 3D simulations, based on the unsteady Reynolds-Averaged Navier-Stokes equations, show consistent advantages as presented herein. A Proper Orthogonal Decomposition was used to characterize the four most energetic modes of the meandering jet at the free surface level, allowing comparison against experimental data and 2D (depth-averaged) numerical results. Three different isotropic eddy viscosity models (RNG k-ε, k-ε, k-ω) were tested. The 3D models accurately predicted the frequency of the modes, whereas the amplitudes of the modes and associated energy were damped for the friction-dominant cases and augmented for non-frictional ones. The performance of the three turbulence models remained essentially similar, with slightly better predictions by RNG k-ε model in the case with the highest Reynolds number. Finally, the Q-criterion was used to identify vortices and study their dynamics, assisting on the identification of the differences between: i) the three-dimensional phenomenon (here reproduced), ii) its two-dimensional footprint in the free surface (experimental observations) and iii) the depth-averaged case (represented by 2D models).}, language = {en} } @article{BungCrookstonValero2020, author = {Bung, Daniel B. and Crookston, Brian M. and Valero, Daniel}, title = {Turbulent free-surface monitoring with an RGB-D sensor: the hydraulic jump case}, series = {Journal of Hydraulic Research}, journal = {Journal of Hydraulic Research}, publisher = {Taylor \& Francis}, address = {London}, issn = {1814-2079}, doi = {10.1080/00221686.2020.1844810}, year = {2020}, language = {en} } @article{KramerValeroChansonetal.2019, author = {Kramer, Matthias and Valero, Daniel and Chanson, Hubert and Bung, Daniel B.}, title = {Towards reliable turbulence estimations with phase-detection probes: an adaptive window cross-correlation technique}, series = {Experiments in Fluids}, volume = {60}, journal = {Experiments in Fluids}, publisher = {Springer}, address = {Berlin}, issn = {1432-1114}, doi = {10.1007/s00348-018-2650-9}, year = {2019}, language = {en} } @article{OertelBung2015, author = {Oertel, Mario and Bung, Daniel B.}, title = {Stability and scour development of bed material on crossbar block ramps}, series = {International journal of sediment research}, volume = {30}, journal = {International journal of sediment research}, number = {4}, publisher = {Elsevier}, address = {Amsterdam}, issn = {1001-6279}, doi = {10.1016/j.ijsrc.2014.12.003}, pages = {344 -- 350}, year = {2015}, abstract = {Block ramps are ecologically oriented drop structures with adequate energy dissipation and partially moderate flow velocities. A special case is given with crossbar block ramps, where the upstream and downstream level difference is reduced by a series of basins. To prevent the total structure from failing, the stability of single boulders within the crossbars and the bed material in between must be guaranteed. The present paper addresses the stability of bed material and scour development for various flow regimes. Any bed material erosion may affect the stability of the crossbar boulders, which in turn can result in major damages of the ramp. Therefore new design approaches are developed to choose an appropriate bed material size and to avoid failures of crossbar block ramp structures.}, language = {en} } @article{ValeroBung2016, author = {Valero, Daniel and Bung, Daniel B.}, title = {Sensitivity of turbulent Schmidt number and turbulence model to simulations of jets in crossflow}, series = {Environmental Modelling and Software}, volume = {82}, journal = {Environmental Modelling and Software}, publisher = {Elsevier}, address = {Amsterdam}, issn = {1364-8152 (electronic)}, doi = {10.1016/j.envsoft.2016.04.030}, pages = {218 -- 228}, year = {2016}, abstract = {Environmental discharges have been traditionally designed by means of cost-intensive and time-consuming experimental studies. Some extensively validated models based on an integral approach have been often employed for water quality problems, as recommended by USEPA (i.e.: CORMIX). In this study, FLOW-3D is employed for a full 3D RANS modelling of two turbulent jet-to-crossflow cases, including free surface jet impingement. Results are compared to both physical modelling and CORMIX to better assess model performance. Turbulence measurements have been collected for a better understanding of turbulent diffusion's parameter sensitivity. Although both studied models are generally able to reproduce jet trajectory, jet separation downstream of the impingement has been reproduced only by RANS modelling. Additionally, concentrations are better reproduced by FLOW-3D when the proper turbulent Schmidt number is used. This study provides a recommendation on the selection of the turbulence model and the turbulent Schmidt number for future outfall structures design studies.}, language = {en} } @article{ValeroChansonBung2019, author = {Valero, Daniel and Chanson, Hubert and Bung, Daniel B.}, title = {Robust estimators for turbulence properties assessment}, pages = {1 -- 24}, year = {2019}, language = {en} } @article{ValeroChansonBung2020, author = {Valero, Daniel and Chanson, Hubert and Bung, Daniel B.}, title = {Robust estimators for free surface turbulence characterization: A stepped spillway application}, series = {Flow Measurement and Instrumentation}, volume = {76}, journal = {Flow Measurement and Instrumentation}, number = {Art. 101809}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0955-5986}, doi = {10.1016/j.flowmeasinst.2020.101809}, year = {2020}, abstract = {Robust estimators are parameters insensitive to the presence of outliers. However, they presume the shape of the variables' probability density function. This study exemplifies the sensitivity of turbulent quantities to the use of classic and robust estimators and the presence of outliers in turbulent flow depth time series. A wide range of turbulence quantities was analysed based upon a stepped spillway case study, using flow depths sampled with Acoustic Displacement Meters as the flow variable of interest. The studied parameters include: the expected free surface level, the expected fluctuation intensity, the depth skewness, the autocorrelation timescales, the vertical velocity fluctuation intensity, the perturbations celerity and the one-dimensional free surface turbulence spectrum. Three levels of filtering were utilised prior to applying classic and robust estimators, showing that comparable robustness can be obtained either using classic estimators together with an intermediate filtering technique or using robust estimators instead, without any filtering technique.}, language = {en} } @article{ValeroBung2018, author = {Valero, Daniel and Bung, Daniel B.}, title = {Reformulating self-aeration in hydraulic structures: Turbulent growth of free surface perturbations leading to air entrainment}, series = {International Journal of Multiphase Flow}, volume = {100}, journal = {International Journal of Multiphase Flow}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0301-9322}, doi = {10.1016/j.ijmultiphaseflow.2017.12.011}, pages = {127 -- 142}, year = {2018}, abstract = {A new formulation for the prediction of free surface dynamics related to the turbulence occurring nearby is proposed. This formulation, altogether with a breakup criterion, can be used to compute the inception of self-aeration in high velocity flows like those occurring in hydraulic structures. Assuming a simple perturbation geometry, a kinematic and a non-linear momentum-based dynamic equation are formulated and forces acting on a control volume are approximated. Limiting steepness is proposed as an adequate breakup criterion. Role of the velocity fluctuations normal to the free surface is shown to be the main turbulence quantity related to self-aeration and the role of the scales contained in the turbulence spectrum are depicted. Surface tension force is integrated accounting for large displacements by using differential geometry for the curvature estimation. Gravity and pressure effects are also contemplated in the proposed formulation. The obtained equations can be numerically integrated for each wavelength, hence resulting in different growth rates and allowing computation of the free surface roughness wavelength distribution. Application to a prototype scale spillway (at the Aviemore dam) revealed that most unstable wavelength was close to the Taylor lengthscale. Amplitude distributions have been also obtained observing different scaling for perturbations stabilized by gravity or surface tension. The proposed theoretical framework represents a new conceptualization of self-aeration which explains the characteristic rough surface at the non-aerated region as well as other previous experimental observations which remained unresolved for several decades.}, language = {en} } @article{BungValero2018, author = {Bung, Daniel B. and Valero, Daniel}, title = {Re-aeration on stepped spillways with special consideration of entrained and entrapped air}, series = {Geosciences}, volume = {8}, journal = {Geosciences}, number = {9}, publisher = {MDPI}, address = {Basel}, issn = {2076-3263}, pages = {Article number 333}, year = {2018}, abstract = {As with most high-velocity free-surface flows, stepped spillway flows become self-aerated when the drop height exceeds a critical value. Due to the step-induced macro-roughness, the flow field becomes more turbulent than on a similar smooth-invert chute. For this reason, cascades are oftentimes used as re-aeration structures in wastewater treatment. However, for stepped spillways as flood release structures downstream of deoxygenated reservoirs, gas transfer is also of crucial significance to meet ecological requirements. Prediction of mass transfer velocities becomes challenging, as the flow regime differs from typical previously studied flow conditions. In this paper, detailed air-water flow measurements are conducted on stepped spillway models with different geometry, with the aim to estimate the specific air-water interface. Re-aeration performances are determined by applying the absorption method. In contrast to earlier studies, the aerated water body is considered a continuous mixture up to a level where 75\% air concentration is reached. Above this level, a homogenous surface wave field is considered, which is found to significantly affect the total air-water interface available for mass transfer. Geometrical characteristics of these surface waves are obtained from high-speed camera investigations. The results show that both the mean air concentration and the mean flow velocity have influence on the mass transfer. Finally, an empirical relationship for the mass transfer on stepped spillway models is proposed.}, language = {en} } @article{ValeroSchalkoFriedrichetal.2021, author = {Valero, Daniel and Schalko, Isabella and Friedrich, Heide and Abad, Jorge D. and Bung, Daniel B. and Donchyts, Gennadii and Felder, Stefan and Ferreira, Rui M. L. and Hohermuth, Benjamin and Kramer, Matthias and Li, Danxun and Mendes, Luis and Moreno-Rodenas, Antonio and Nones, Michael and Paron, Paolo and Ruiz-Villanueva, Virginia and Wang, Ruo-Qian and Franca, Mario J.}, title = {Pathways towards democratization of hydro-environment observations and data}, series = {Iahr White Paper Series}, journal = {Iahr White Paper Series}, number = {1}, publisher = {International Association for Hydro-Environment Engineering and Research (IAHR)}, pages = {1 -- 9}, year = {2021}, language = {en} } @article{BungValero2016, author = {Bung, Daniel B. and Valero, Daniel}, title = {Optical flow estimation in aerated flows}, series = {Journal of Hydraulic Research}, volume = {54}, journal = {Journal of Hydraulic Research}, number = {5}, publisher = {Taylor \& Francis}, address = {London}, doi = {10.1080/00221686.2016.1173600}, pages = {575 -- 580}, year = {2016}, abstract = {Optical flow estimation is known from Computer Vision where it is used to determine obstacle movements through a sequence of images following an assumption of brightness conservation. This paper presents the first study on application of the optical flow method to aerated stepped spillway flows. For this purpose, the flow is captured with a high-speed camera and illuminated with a synchronized LED light source. The flow velocities, obtained using a basic Horn-Schunck method for estimation of the optical flow coupled with an image pyramid multi-resolution approach for image filtering, compare well with data from intrusive conductivity probe measurements. Application of the Horn-Schunck method yields densely populated flow field data sets with velocity information for every pixel. It is found that the image pyramid approach has the most significant effect on the accuracy compared to other image processing techniques. However, the final results show some dependency on the pixel intensity distribution, with better accuracy found for grey values between 100 and 150.}, language = {en} } @article{ZhangValeroBungetal.2018, author = {Zhang, G. and Valero, Daniel and Bung, Daniel B. and Chanson, H.}, title = {On the estimation of free-surface turbulence using ultrasonic sensors}, series = {Flow Measurement and Instrumentation}, volume = {60}, journal = {Flow Measurement and Instrumentation}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0955-5986}, doi = {10.1016/j.flowmeasinst.2018.02.009}, pages = {171 -- 184}, year = {2018}, abstract = {Accurate determination of free-surface dynamics has attracted much research attention during the past decade and has important applications in many environmental and water related areas. In this study, the free-surface dynamics in several turbulent flows commonly found in nature were investigated using a synchronised setup consisting of an ultrasonic sensor and a high-speed video camera. Basic sensor capabilities were examined in dry conditions to allow for a better characterisation of the present sensor model. The ultrasonic sensor was found to adequately reproduce free-surface dynamics up to the second order, especially in two-dimensional scenarios with the most energetic modes in the low frequency range. The sensor frequency response was satisfactory in the sub-20 Hz band, and its signal quality may be further improved by low-pass filtering prior to digitisation. The application of the USS to characterise entrapped air in high-velocity flows is also discussed.}, language = {en} } @article{OertelBung2015, author = {Oertel, Mario and Bung, Daniel B.}, title = {Numerische Str{\"o}mungssimulationen von Fließgew{\"a}ssern : Praxisanwendungen und zuk{\"u}nftige Entwicklungen}, series = {Korrespondenz Wasserwirtschaft : KW}, volume = {8}, journal = {Korrespondenz Wasserwirtschaft : KW}, number = {H. 3}, publisher = {Gesellschaft zur F{\"o}rderung der Abwassertechnik}, address = {Hennef}, issn = {1616-430X}, pages = {177 -- 182}, year = {2015}, language = {de} } @article{Bung2013, author = {Bung, Daniel B.}, title = {Non-intrusive detection of air-water surface roughness in self-aerated chute flows}, series = {Journal of hydraulic research}, volume = {Vol. 51}, journal = {Journal of hydraulic research}, number = {Iss. 3}, publisher = {Taylor \& Francis}, address = {London}, issn = {1814-2079 (E-Journal); 0022-1686 (Print)}, pages = {322 -- 329}, year = {2013}, language = {en} } @article{LeandroBungCarvalho2014, author = {Leandro, J. and Bung, Daniel B. and Carvalho, R.}, title = {Measuring void fraction and velocity fields of a stepped spillway for skimming flow using non-intrusive methods}, series = {Experiments in fluids}, journal = {Experiments in fluids}, number = {55}, publisher = {Springer Nature}, address = {Heidelberg}, issn = {0723-4864 (Print) ; 1432-1114 (Online)}, doi = {10.1007/s00348-014-1732-6}, pages = {Art. 1732}, year = {2014}, language = {en} } @article{OertelBung2012, author = {Oertel, Mario and Bung, Daniel B.}, title = {Initial stage of two-dimensional dam-break waves: laboratory versus VOF}, series = {Journal of hydraulic research}, volume = {50}, journal = {Journal of hydraulic research}, number = {1}, publisher = {Taylor \& Francis}, address = {London}, issn = {1814-2079 (E-Journal); 0022-1686 (Print)}, doi = {10.1080/00221686.2011.639981}, pages = {89 -- 97}, year = {2012}, abstract = {Since several decades, dam-break waves have been of main research interest. Mathematical approaches have been developed by analytical, physical and numerical models within the past 120 years. During the past 10 years, the number of research investigations has increased due to improved measurement techniques as well as significantly increased computer memories and performances. In this context, the present research deals with the initial stage of two-dimensional dam-break waves by comparing physical and numerical model results as well as analytical approaches. High-speed images and resulting particle image velocimetry calculations are thereby compared with the numerical volume-of-fluid (VOF) method, included in the commercial code FLOW-3D. Wave profiles and drag forces on placed obstacles are analysed in detail. Generally, a good agreement between the laboratory and VOF results is found.}, language = {en} } @article{ErpicumCrookstonBombardellietal.2021, author = {Erpicum, Sebastien and Crookston, Brian M. and Bombardelli, Fabian and Bung, Daniel B. and Felder, Stefan and Mulligan, Sean and Oertel, Mario and Palermo, Michele}, title = {Hydraulic structures engineering: An evolving science in a changing world}, series = {Wires Water}, volume = {8}, journal = {Wires Water}, number = {2}, publisher = {Wiley}, address = {Weinheim}, issn = {2049-1948}, doi = {10.1002/wat2.1505}, year = {2021}, language = {en} } @article{Bung2011, author = {Bung, Daniel B.}, title = {Fließcharakteristik und Sauerstoffeintrag bei selbstbel{\"u}fteten Gerinnestr{\"o}mungen auf Kaskaden mit gem{\"a}ßigter Neigung}, series = {{\"O}sterreichische Wasser- und Abfallwirtschaft}, volume = {Vol. 63}, journal = {{\"O}sterreichische Wasser- und Abfallwirtschaft}, number = {Iss. 3-4}, publisher = {Springer}, address = {Berlin}, issn = {1613-7566 (E-Journal); 0945-358X (Print)}, pages = {76 -- 81}, year = {2011}, language = {de} } @article{KerpenBungValeroetal.2017, author = {Kerpen, Nils B. and Bung, Daniel B. and Valero, Daniel and Schlurmann, Torsten}, title = {Energy dissipation within the wave run-up at stepped revetments}, series = {Journal of Ocean University of China}, volume = {16}, journal = {Journal of Ocean University of China}, number = {4}, publisher = {Springer}, address = {Berlin}, issn = {1993-5021}, doi = {10.1007/s11802-017-3355-z}, pages = {649 -- 654}, year = {2017}, language = {en} } @article{ValeroBungCrookston2018, author = {Valero, Daniel and Bung, Daniel B. and Crookston, B.M.}, title = {Energy dissipation of a Type III basin under design and adverse conditions for stepped and smooth spillways}, series = {Journal of Hydraulic Engineering}, volume = {144}, journal = {Journal of Hydraulic Engineering}, number = {7}, publisher = {ASCE}, address = {Reston, Va.}, issn = {0733-9429}, doi = {10.1061/(ASCE)HY.1943-7900.0001482}, year = {2018}, abstract = {New information regarding the influence of a stepped chute on the hydraulic performance of the United States Bureau of Reclamation (Reclamation) Type III hydraulic jump stilling basin is presented for design (steady) and adverse (decreasing tailwater) conditions. Using published experimental data and computational fluid dynamics (CFD) models, this paper presents a detailed comparison between smooth-chute and stepped-chute configurations for chute slopes of 0.8H:1V and 4H:1V and Froude numbers (F) ranging from 3.1 to 9.5 for a Type III basin designed for F = 8. For both stepped and smooth chutes, the relative role of each basin element was quantified, up to the most hydraulic extreme case of jump sweep-out. It was found that, relative to a smooth chute, the turbulence generated by a stepped chute causes a higher maximum velocity decay within the stilling basin, which represents an enhancement of the Type III basin's performance but also a change in the relative role of the basin elements. Results provide insight into the ability of the CFD models [unsteady Reynolds-averaged Navier-Stokes (RANS) equations with renormalization group (RNG) k-ϵ turbulence model and volume-of-fluid (VOF) for free surface tracking] to predict the transient basin flow structure and velocity profiles. Type III basins can perform adequately with a stepped chute despite the effects steps have on the relative role of each basin element. It is concluded that the classic Type III basin design, based upon methodology by reclamation specific to smooth chutes, can be hydraulically improved for the case of stepped chutes for design and adverse flow conditions using the information presented herein.}, language = {en} } @article{ValeroBung2016, author = {Valero, Daniel and Bung, Daniel B.}, title = {Development of the interfacial air layer in the non-aerated region of high-velocity spillway flows: Instabilities growth, entrapped air and influence on the self-aeration onset}, series = {International Journal of Multiphase Flow}, volume = {84}, journal = {International Journal of Multiphase Flow}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0301-9322}, doi = {10.1016/j.ijmultiphaseflow.2016.04.012}, pages = {66 -- 74}, year = {2016}, abstract = {Self-aeration is traditionally explained by the water turbulent boundary layer outer edge intersection with the free surface. This paper presents a discussion on the commonly accepted hypothesis behind the computation of the critical point of self-aeration in spillway flows and a new formulation is proposed based on the existence of a developing air flow over the free surface. Upstream of the inception point of self-aeration, some surface roughening has been often reported in previous studies which consequently implies some entrapped air transport and air-water flows coupling. Such air flow is proven in this study by presenting measured air velocities and computing the air boundary layer thickness for a 1V:2H smooth chute flow. Additionally, the growth rate of free surface waves has been analysed by means of Ultrasonic Sensors measurements, obtaining also the entrapped air concentration. High-speed camera imaging has been used for qualitative study of the flow perturbations.}, language = {en} } @article{Bung2011, author = {Bung, Daniel B.}, title = {Developing flow in skimming flow regime on embankment stepped spillways}, series = {Journal of hydraulic research}, volume = {Vol. 49}, journal = {Journal of hydraulic research}, number = {Iss. 5}, publisher = {Taylor \& Francis}, address = {London}, issn = {1814-2079 (E-Journal); 0022-1686 (Print)}, pages = {639 -- 648}, year = {2011}, language = {en} } @article{ValeroBungCrookston2019, author = {Valero, D. and Bung, Daniel B. and Crookston, B. M.}, title = {Closure to "Energy Dissipation of a Type III Basin under Design and Adverse Conditions for Stepped and Smooth Spillways"}, series = {Journal of Hydraulic Engineering}, volume = {146}, journal = {Journal of Hydraulic Engineering}, number = {2}, publisher = {ASCE}, address = {Reston, Va.}, doi = {10.1061/(ASCE)HY.1943-7900.0001669}, year = {2019}, language = {en} } @article{ValeroBung2017, author = {Valero, Daniel and Bung, Daniel B.}, title = {Artificial Neural Networks and pattern recognition for air-water flow velocity estimation using a single-tip optical fibre probe}, series = {Journal of Hydro-environment Research}, volume = {19}, journal = {Journal of Hydro-environment Research}, number = {3}, publisher = {Elsevier}, address = {Amsterdam}, issn = {1570-6443}, doi = {10.1016/j.jher.2017.08.004}, pages = {150 -- 159}, year = {2017}, language = {en} } @article{LopesLeandroCarvalhoetal.2017, author = {Lopes, Pedro and Leandro, Jorge and Carvalho, Rita F. and Bung, Daniel B.}, title = {Alternating skimming flow over a stepped spillway}, series = {Environmental Fluid Mechanics}, volume = {17}, journal = {Environmental Fluid Mechanics}, number = {2}, publisher = {Springer}, address = {Berlin}, issn = {1573-1510}, doi = {10.1007/s10652-016-9484-x}, pages = {303 -- 322}, year = {2017}, language = {en} }